The present invention relates to an oil pressure control apparatus of a belt-driven continuously variable transmission.
As a continuously variable transmission provided in a vehicle, a belt-driven continuously variable transmission is known in which a belt is clamped with oil pressure to transmit motive power, and a gear ratio is changed by changing a belt hanging radius.
In an oil pressure control apparatus of this sort of belt-driven continuously variable transmission, many control valves of various types, electromagnetic valves that control those control valves, and the like are provided. For example, valves provided include a line oil pressure control valve that regulates a line oil pressure that becomes the source pressure for the oil pressure of various parts; a gear oil pressure control valve that regulates the line oil pressure that becomes the source pressure, and supplies a gear oil pressure that controls a gear ratio of the belt-driven continuously variable transmission to a driving-side pulley (primary pulley) of the belt-driven continuously variable transmission; a clamping oil pressure control valve that likewise regulates the line oil pressure that becomes the source pressure, and supplies a clamping oil pressure that controls belt clamping of the belt-driven continuously variable transmission to a driven-side pulley (secondary pulley) of the belt-driven continuously variable transmission; and the like. Also provided are linear electromagnetic valves, ON-OFF electromagnetic valves, or the like for controlling each of these control valves.
An oil pressure control apparatus of a belt-driven continuously variable transmission is disclosed in JP H3-213773A (referred to below as Patent Document 1) and JP 2006-153104A (referred to below as Patent Document 2). In Patent Document 2, there is a description of control in a case where an electromagnetic valve that controls a gear oil pressure control valve or an electromagnetic valve that controls a clamping oil pressure control valve has failed.
Incidentally, in the oil pressure control apparatus, in each valve or the electromagnetic valve that controls that valve, there may be a mechanical failure of such as a stuck valve, or there may be a failure due to an electrical cause, such as a wire disconnection or a short circuit in an electromagnetic valve. In a conventional oil pressure control apparatus of a belt-driven continuously variable transmission, due to having a configuration in which a gear oil pressure is supplied to a driving-side pulley only from a gear oil pressure control valve, when the gear oil pressure control valve or the electromagnetic valve that controls that valve fails, the gear oil pressure that controls the gear ratio suddenly drops, and as a result, there is a possibility of falling into a state of sudden deceleration. Also, with sudden deceleration there is a possibility that belt slippage or an excessive shock will occur.
In order to avoid this sort of sudden deceleration when a failure occurs, the oil pressure control apparatus can be provided with a control valve having a backup function, for example. However, in this case, a separate electromagnetic valve or the like is necessary in order to control the control valve having the backup function, so there is also the problem of increased cost and size of the apparatus.
In above Patent Document 1, there is no disclosure with respect to compatibility with occurrence of such a failure. In Patent Document 2, there is a description of a case where an electromagnetic valve that controls a gear oil pressure control valve has failed, but there is no disclosure with respect to compatibility with a case where the gear oil pressure control valve itself has failed.
The present invention was made in view of such problems, and it is an object thereof to provide an oil pressure control apparatus in which, without adding a new electromagnetic valve, it is possible to avoid the occurrence of a state of sudden deceleration even when, for example, a gear oil pressure control valve has failed.